Single-crystal elasticity of stishovite: New experimental data obtained using high-frequency resonant ultrasound spectroscopy and a Gingham check structure model

Abstract

Single-crystal elasticity of stishovite was examined using a new experimental technique and an empirical macroscopic model. Employing high-frequency resonant ultrasound spectroscopy, single-crystal elastic constants of stishovite were determined: C 11 = 443(3), C 33 = 781(4), C 12 = 193(2), C 23 = 199(2), C 44 = 256(2), and C 33 = 316(2) GPa. The frequency range of the resonant ultrasound spectroscopy techniques was 6–20 MHz, which is much lower than the ∼10 GHz range of the Brillouin scattering technique. Of the elastic constants, the shear elastic constants C 44 and C 66 are consistent with the average value of the previously mentioned Brillouin scattering. Conversely, the four elastic constants, C 11, C 33, C 12, and C 23, slightly deviate outside the range of previous Brillouin scattering results. The present results, except those for C 12, are consistent with recent lattice dynamic analysis of inelastic X-ray scattering data. The adiabatic bulk modulus was calculated as 298 GPa, which is smaller and more consistent with the result of compression experiments than any other Brillouin scattering results (301–312 GPa). The present result shows greater P-wave velocity anisotropy (24.7%) than any preceding work. To understand the unique elastic properties of stishovite, the Gingham check model was proposed and examined. The result shows that the octahedron of 6-coordinated Si in stishovite crystal has stiffness comparable to that of diamond.